doc: sandbox: Fix up dependencies

These are out of date. Update them and point to the existing build
instructions to avoid duplication. Add a few that are missing.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/arch/sandbox.rst b/doc/arch/sandbox.rst
index 9e23e16..f8804e1 100644
--- a/doc/arch/sandbox.rst
+++ b/doc/arch/sandbox.rst
@@ -43,11 +43,7 @@
 Prerequisites
 -------------
 
-Here are some packages that are worth installing if you are doing sandbox or
-tools development in U-Boot:
-
-   python3-pytest lzma lzma-alone lz4 python3 python3-virtualenv
-   libssl1.0-dev
+Install the dependencies noted in :doc:`../build/gcc`.
 
 
 Basic Operation